Photoelectric relay



y 30, 1939' F. H. SHEPARD. JR 2,160,037

PHOTOELECTRIC RELAY Filed June 50, 1937 6 7 23 22 5 9 i L). g,

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Y INVENTOR FR 676' H. SHEPARQJR. fliw ATTORNEY Pam's May 30, 1939 UNITED STATES PATENT OFFICE PHOTOELECTRIC RELAY Delaware Application June 30, 1937, Serial No. 151,159

2 Claims.

My invention relates to photoelectric relays, particularly circuits for coupling light responsive devices, such as photo-tubes, to mechanical or electrical relays.

5 The usual direct current amplifier for amplifying photo-tube currents to a sufiiciently high level to operate large electromagnetic relays is costly to make, difficult to adjust, and unstable in operation, and the direct current power sources for energizing the circuits are expensive to make and maintain. Light responsive devices of this type are particularly unsuited for operation where short flashes or impulses of light must control circuits of considerable power.

An object of my invention is to make an alternating current energized photoelectric relay which will control considerable power in response to short impulses of light.

Another object of my invention is to make a quick acting photoelectric relay that is'stable in operation, easy to adjust, and inexpensive to manufacture.

A photoelectric relay circuit constructed according to my invention may be energized by 5 alternating current of commercial frequency and voltage. An amplifier of the grid controlled type is so connected with a condenser and an alternating voltage source in the grid circuit that an alternating current voltage is impressed between the grid and cathode and, because of the rectifying action of these two electrodes, a negative charge accumulates on the grid and the connected plate of the condenser. This negative charge on the grid is permitted to drain or leak ofi through a photo-tube at a rate proportional to the intensity of light upon the photo-tube. A second amplifier with a grid connected to the cathode of the first amplifier is also provided with a condenser between its grid and a point on an alternating current circuit such as the heating circuit of its cathode to bias the grid preferably to cut-off. An impulse of light upon the photo-tube momentarily reduces the negative v bias upon the grid of the first amplifier causing a discharge of the condenser in the grid circuit of the second amplifier and the release in the anode cathode circuit and the series load circuit 01' the second amplifier of an appreciable electronic discharge, which continues until the condenser of the second amplifier is sufliclently recharged to restore the grid to a cut-off or negative potential to interrupt the anode current. The circuits constructed according to my invention will produce a large current flow in the outso put circuit of the second amplifier and through a relay winding or any desired loading device in response to a short fiash or impulse of light on the photo-tube.

Specific features of my invention are pointed out with particularity in the appended claims and preferred embodiments of my invention are described in the following specification and the accompanying drawing in which Figure 1 is a circuit diagram of my novel photoelectric relay embodying the characteristic features of my invention; and Figure 2 is a circuit diagram of a modified photoelectric. relay embodying my invention.

The circuits of photo-tube l and amplifier 2 with anode 3, grid 4, cathode 5, and heater 6 are 15 energized by an alternating current source of commercial frequency and voltage through lines I and l. The circuits of amplifier 8 with anode 9, grid l0, cathode II, and heater I2 are also energized by the a.c. source, the anode being connected to one side of the source through a load impedance l3 shown schematically as the windings of an electromagnetic relay. Heaters 6 and I! are, respectively, coupled through transformers ll and I5, whose primaries may be connected to a.c. source 1, l, the connections between the source and the transformers being omitted for the sake of clarity in the drawing.

A negative bias may be produced on grid 4 of amplifier 2 by condenser l6 connected on the one hand to an adjustable contact on potentiometer Il across the heater and on the other through resistance I8 to the grid. It is apparent that a. potential proportional to the heater a.c. voltage is impressed between the grid and cathode and that because of the rectifying action of these two electrodes, the upper plate of condenser IE will assume a negative direct current potential with respect to the other plate proportional to the distance of the movable contact from the lower end of resistance ll. With the cathode of photo-tube i connected to the grid and the anode connected to the a.--c. supply line I, it is adapted, when illuminated, to drain ofi the charge on the condenser and to reduce the negative bias on the grid, thus increasing the flow of current in the anode circuit of amplifier 2. Since the anode circuit of amplifier 2 is completed to the lower conductor 1 of the a.c. supply line through the grid-cathode impedance i0ll of amplifier 8 and the parallel condenser IS, a change in space current through amplifier 2 afiects the charge on condenser I9 and the grid bias potential of grid 10. Resistor 20 is connected between grid I0 and condenser i8 to determine the time constant of the condenser-grid-cathode circuit of tube 8, and

is connected at its ends to the contacts 2| and 22 of the single pole double throw switch, the movable contactor 23 of which is connected to the cathode 5.

With photo-tube 1 dark, and transformers I4 and I5 energized to heat their cathodes, alternating current potentials are impressed on the grids which, through the rectifying action or the grid circuits, fully charge each of the condensers and bias tube 8 preferably to cut-oif and tube 2 to some low value of anode current. If, now, a short flash or impulse of light falls upon phototube I, while a.c. line 1 is positive with respect to l, a momentary rise in a positive direction or the potential of grid 4 results, causing a momentary increase in the anode current through tube 2. With the switch contactor on pole 2|, this increase in anode current or reduction of effective anode-cathode resistance carries cathode 5 and connected grid 40' to a more positive potential and initiates a large anode current through tube 8 and its load impedance l3. The charge on condenser 69 at the same time is suddenly reduced, the stored energy in the condenser being drawn off through the anode-cathode space of amplifier 2. Even after the extinction of light on the photo-tube and the recession of space current through tube 2, condenser it, which may have an appreciable capacity, continues to hold the grid ill or" tube 8 at a potential which permits the continued flow of anode current through tube 8, this current being cut-oil only after condenser i9 is recharged by several cycles of. power in the heater circuit 52. Accordingly, a short impulse of light upon the photo-tube will create a long-lived impulse of current through the windings of relay H3.

The grid controlled anode-cathode space of tube 2 functions much the same as a switch for selectively connecting, in response to light pulses, a positive potential to the grid of ampliher 3, so that by placing contactor 23 on 22 to connect grid l0 directly to cathode 5, the anode current of tube 8 may he suddenly turned on and off in response to flashes of light upon the phototube, the duration of the anode cur= rent being accurately measured within the cycle of the supply frequency by the duration of the light impulses. The closing of the electron switch 2 immediately impresses upon grid ID a positive potential which starts the anode current simultaneously with the beginning of the light impulses, and with the time constant of the grid circuit greater than the duration of the light impulse, grid I0 may immediately be swung to cutoff potential upon the open circuiting of electron switch 2. My novel circuit, thus operated, may advantageously be employed in controlling registers, sorting machines and other devices where quick and positive action is required in the output relay.

Since the cathode 5 and its heater circuit are effectively isolated from ground by the filament ransformer M, the cathode and its directly connected elements, including the lower plate of condenser l6, rise in potential upon the initiation of current through amplifier 2. Accordingly, the necessary voltage drop across resistor 18 to effeet a predetermined shift in the potential of grid 4 by current flowing through the phototube is less than if the photo-tube load IS in series with IE were returned to ground or prevented from shifting in potential. It may be desired, however, to eliminate the filament transformer for the less expensive heating circuit shown in Figure 2. In this case, resistor I! may be relatively large or the order of 1 megohm to provide a large resistance drop between the adjustable contact thereon and the ground. The cathodes may, if desired, be of the direct heated or filamentary types.

Good results have been obtained with a circuit constructed according to Figure 1, where the photo-tube is of the type commercially known as the 919; amplifier 2 as the type known as the 6F5; and amplifier 8 as type 25A6, 25L6 or 43; and with resistor I8, 10 megohms; condenser IS, micromicroiarads; resistor H, 5000 ohms; resistor 20, 100,000 ohms; and condenser 19, .Ol rnicrofarad.

A photoelectric relay constructed according to my invention is capable oi controlling short or long impulses of power of considerable magnitude in response to short impulses of. light. My improved photoelectric relay is stable in operation, easy to adjust, and inexpensive to manuracture.

I claim:

1. A photoelectric relay comprising an alterhating current source, an amplifier tube with an anode, a grid, and a cathode, and an alternating current circuit coupled to said source for heating said cathode, a load impedance, said anode and cathode being connected to opposite sides of said source through said impedance, a COllClEDSGi and a resistor connected in series between said grid and one side of the heating circuit for impressing upon said grid an alternating current voltage, the resistor being connected to said grid, a thermionic amplifier with an anode, grid, cathode, and an alternating current heating circuit for said cathode, the anode-cathode circuit of said amplifier being connected between one side of said source and one end of said resistor, a second resistor and a second condenser connected hctween the grid. and one side oi? said heating circuit for negatively biasing the grid of ther mionic amplifier, and a photo-tube with its anode connected to said one side of said source and photocathode connected to the grid of said thermionic amplifier.

2. A. photoelectric relay comprising an alternating current source, an amplifier tube with an anode, a grid and a cathode, and a heater with an alternating current heating circuit for said cathode, a load impedance in series with the plate circuit of said amplifier tube connected across said source, means to minimize the flow of current through said impedance comprising a resistor connected at one end to said grid and a condenser connected between one side of said heating circuit and the other end of said resistor; means to initiate a large and sustained current flow in said impedance in response to a flash of light comprising a thermionic amplifier with an anode, grid, cathode and a heater with an alternating current heating circuit for said cathode, the anode-cathode circuit of said amplifier being connected between one side of said source and one end of said resistor, a second resistor connected at one end to the grid of said amplifier, the other end being connected through a condenser to one side of the cathode heating circuit of said amplifier, and a phototube with a photocathode and an anode, the anode being connected to said one side of said source and the cathode being connected to the grid of said amplifier.

FRANCIS H. SHEPARD, JR. 

